Field of the Invention
The present invention relates to a system and a method for counting aerosol particles in the atmosphere with respect to each particle size, and more particularly, to a system and a method for counting the aerosol particles by appropriately setting a ratio of flow rate of sample gas and sheath gas.
Description of the Related Art
In the atmosphere, “aerosol particles” which are fine liquid or solid particles are suspended. As these aerosol particles, ISO 15900:2009 targets at aerosol particles whose particle size is 1 nm to 1 μm. To count the aerosol particles having several nm to 1 μm particle sizes, an aerosol particle measuring device is used. The aerosol particle measuring device includes, for example, a differential mobility analyzer (DMA) and a condensation particle counter (CPC), or the DMA and a Faraday cup aerosol electrometer (FCAE). The CPC or the FACE measures the aerosol particles classified out by the DMA, whereby it is possible to count the aerosol particles with respect to each particle size by using the result of the measurement.
In the case where the DMA is used for the classifying, the aerosol particles include not only singly charged aerosol particles whose particle size is relatively small but also multiply (doubly, triply, . . . ) charged aerosol particles whose particle size is relatively large. Therefore, in the measurement, it is assumed that the aerosol particles classified out by the DMA are singly charged and a lognormal distribution holds true in a relation between the particle size and quantity, and the counting result is corrected regarding the quantity of the multiply charged aerosol particles and then particle size distribution is calculated. In the correction, an approximate expression of Wiedensohler or the like is employed as an existence probability of charged number.
Generally, when the DMA is used, multiply charged particles exist for one particle size and when the classifying is performed based on the same electrical mobility, there exist multiply charged particles with different particle sizes. Further, it is known that a variation in the classifying based on the electrical mobility is influenced by flow rates of the aerosol particles and sheath gas in the DMA.